Decussation (or decussatio) is used in biological contexts to describe a crossing, as in the letter X,[1] particularly of nerve fibres, reflecting the contralateral organization of the body.
Examples include:

In the brain, where nerve fibers cross from one lateral part to the other, particularly in the midbrain

Here, a decussation refers to the crossing of millions of axons. To achieve this, there needs to be a tight control in order to have as few errors as possible. The advantage of having such a complicated system may be to compensate for the 180 degree inversion in visual perception through the eye.[2] In addition, it may provide a more robust structure.[3]